1. Field of the Invention
The present invention relates to an optical apparatus, such as a single lens reflex camera, capable of providing superimposed displays in focal point detection regions for automatic focusing.
2. Description of the Related Art
Known cameras capable of superimposed display are disclosed in Japanese Patent Laid-Open Nos. 1-277225 and 5-333259 (corresponding to U.S. Pat. No. 5,579,079). In such a known camera, fluxes of light emitted from an illuminating unit disposed in front of a pentaprism are reflected at a quick return mirror including a half mirror via a projection lens and illuminates a plurality of display units on a focusing screen.
Japanese Patent Laid-Open No. 4-278931 discloses a method for illuminating display bodies on a focusing screen with light emitted from an illuminating unit disposed in the front portion of a pentaprism and transmitting the light through the pentaprism. Japanese Patent Laid-Open No. 10-048733 discloses a camera that includes an information display for displaying shutter speed and aperture disposed in a viewfinder. This information display includes a distance-measuring point display unit corresponding to the actual distance-measuring point.
The cameras disclosed in Japanese Patent Laid-Open Nos. 1-277225 and 5-333259 have a long light path from the illuminating unit to the focusing screen. Moreover, since the fluxes of light are refracted and reflected repeatedly by the projection lens and the main mirror and since the main mirror is a half mirror, the efficiency of light-guiding is low. Therefore, the amount of space required for the illuminating unit becomes large. Furthermore, since such a camera requires adjustment, the size of the camera body increases, productivity decreases, and production cost increases. When focus point detection frames are illuminated using light from light-emitting diodes (LEDs), there is no problems in photographing in a lighted area. However, when photographing in a darker area, the LED light is too bright and irritates the photographer's eyes.
The camera disclosed in Japanese Patent Laid-Open No. 4-278931 transmits light through the pentaprism to illuminate the focusing screen. Therefore, the light path is short and light-guiding efficiency is high. However, since the illuminating unit is disposed in the front portion of the pentaprism, it becomes difficult to dispose a flash-emitting device inside the camera on the front portion of the pentaprism. Since the display on the focusing screen is a mirror, the display does not transmit light from the object. Therefore, when the photographer looks into the viewfinder, the viewfinder is blacked out and it becomes difficult to see the object when the object includes two parallel lines and/or a cross. The surface of the mirror is prepared by depositing a metal film, and therefore, production cost is high. Furthermore, if the metal film for the mirror is deposited in an area displaced from the desired area, an inclined surface and the deposited area are misaligned and thus visibility becomes low.
The camera disclosed in Japanese Patent Laid-Open No. 10-048733 includes an information display, which is used for displaying shutter speed and aperture, disposed outside of the field of view of a known viewfinder. This information display includes a distance-measuring point display unit corresponding to an actual distance-measuring point. In this way, the selected distance-measuring point can be displayed without increasing the production cost of the camera. However, there is a difference in the distance-measuring point displayed and the actual distance-measuring point. For this reason, the visibility of the display is not satisfactory.
By taking into consideration the problems described above, a camera that provides excellent superimposed displays has been provided by the assignee (Japanese Patent Laid-Open No. 2004-085808). This camera is small and can be produced at low cost. Moreover, productivity is improved because the camera does not require adjustment of the light used for illumination.
FIGS. 15 and 16 illustrate the main parts of the camera disclosed in Japanese Patent Laid-Open No. 2004-085808. FIG. 15 is a perspective view illustrating a known method for emitting light for superimposed displays. FIG. 16 is an enlarged view of the known reflection unit illustrated in FIG. 15. The camera illustrated in FIGS. 15 and 16 includes an automatic focus (AF) device having a plurality of focal point detection regions and superimposed displays corresponding to the plurality of focal point detection regions for automatic focusing. A light source is disposed on the side of a focusing screen closer to the eyepiece. Moreover, superimposed display patterns 70 for displaying the points corresponding to the plurality of focal point detection regions are provided on the eyepiece-side of the focusing screen. The superimposed display patterns 70 each includes a reflective angle-forming surface group 80 and a light-reflecting surface-processed unit 90 (an area that has been coated with a reflective metal) having a smaller surface area than the reflective angle-forming surface group 80. The superimposed display patterns 70 are irradiated with light from the light source to provide superimposed displays for automatic focusing.